USB 2.0 vs USB 3.0

Lots of people are asking the question as to why many manufacturers do not produce interfaces that specifically utilise the USB 3.0 protocol.

Firstly, although USB 3.0 offers greater bandwidth than USB 2.0, it will deliver no round trip latency benefits over USB 2.0. This is due to the architecture of the host computer driver stack and its handling of USB audio (isochronous) data. The stack schedules data transfers to and from audio drivers at millisecond frame intervals which means that, no matter how fast the data moves over the USB bus, this defines the limit on minimum latency achievable.

A good analogy is to think of it as a drainpipe and a tennis ball. The tennis ball is the data and the width of the pipe signifies available bandwidth. With the drainpipe set at the same gradient, letting go of the ball at the top of the drainpipe will see it arrive at the bottom in a given amount of time. That's your latency, the time it takes to go from end to end.

USB 3.0 offers a much wider pipe, which in terms of the analogy, means that it could allow a greater number tennis balls (more data) to travel down the pipe, but the balls would not travel down the pipe any faster. This is the same when comparing USB 3.0 and USB 2.0 in terms of the way they transfer audio data.

This is not to say that the higher band width offered by USB 3.0 does not have added benefit in some situations, however, for our largest channel count USB audio interface, the Scarlett 18i20, USB 2.0 provides more than enough bandwidth for delivering 18 channels of audio inputs and 20 channels of audio outputs simultaneously.

There is also a question of backwards compatibility. Currently, most computers still come with USB 2.0 ports as well as USB 3.0, and many users still work on systems that have no USB3.0 connectivity at all. USB 2.0 devices work without any issue on USB 3.0 ports, however the same cannot be said for USB 3.0 devices on USB 2.0 ports.

With the question about backwards compatibility, combined with no real benefits to round-trip latency performance, the USB 2.0 protocol is still the most efficient technology for professional multichannel recording for the channel counts our USB devices provide.